1. Field of the Invention
The present invention generally relates to reducing undesirable acoustic noise generated by a hard disk drive. More particularly, the present invention relates to a disk drive employing spindle motor commutation time variation for reducing acoustic noise in the disk drive.
2. Description of the Prior Art
In hard disk drives, data is stored on magnetic media disks, which are typically stacked on a spindle assemble. The spindle assembly is mechanically coupled to a spindle motor which rotates the disks at a substantially constant operating spin-rate during an operating mode of the disk drive.
A typical three-phase spindle motor includes a stator having three windings and a rotor. The rotor has magnets that provide a permanent magnet field. The spindle motor can generate torque on the rotor when current flows through at least one of the windings. The torque depends on the magnitude and direction of current flow through the windings and an angular position of the rotor relative to the stator. The functional relationship between torque and current flow and angular position is commonly depicted in a set of torque curves, each of which corresponds to a respective one of a series of commutation states.
A spindle motor driver typically drives the spindle motor. The spindle motor driver includes a commutation state sequencer having a sequence of commutation states for generating a sequence of control signals. The spindle motor driver also includes switching elements which are responsive to the sequence of control signals for sequentially applying a voltage across the selected combinations of the windings of the spindle motor to generate positive torque on the rotor to maintain the operating spin-rate. A spindle motor control system provides a series of commutation clock pulses to advance the commutation state sequencer from a present commutation state to a next commutation state. The series of commutation clock pulses have a corresponding series of commutation clock periods. In conventional disk drives, the commutation clock periods each have a nominal commutation clock period that depends on the operating spin-rate. The nominal commutation clock period produced by the conventional spindle motor control system cause the spindle motor to be commutated at fixed time intervals.
Typical disk drives produce acoustic noise to a large extent from mechanically induced vibrations. Some portion of the acoustic noise produced in the disk drive is from electro-magnetically induced vibrations. The electro-magnetically induced vibrations occur mainly at harmonics of the spindle motor fixed commutation frequency resulting from the nominal commutation clock period. The spindle motor commutation fixed time intervals provide for reliable detection of back electromotive force (BEMF) zero crossings, and provide for the spindle motor to be synchronously operated at the proper nominal commutation frequency. The conventional spindle motor control system produces spindle motor commutation harmonics occurring at fixed frequencies. The commutation harmonics occurring at fixed frequencies cause narrow peaks in the acoustic spectrum known as prominent tones. The prominent tones can be audible and can potentially violate disk drive acoustic noise specifications.
There exists substantial competitive pressure to develop mass-market hard disk drives having reduced acoustic noise. For the reasons stated above, there is a need to reduce undesirable acoustic noise generated by a hard disk drive, especially the acoustic noise produced from electro-magnetically induced vibrations occurring mainly at harmonics of the spindle motor commutation frequency.
The invention can be regarded as a disk drive that incidentally generates undesirable acoustic noise during an operation mode. The disk drive includes a spindle motor, switching elements, a commutation state sequencer, and a spindle motor control system. The spindle motor has a plurality of windings and a rotor rotatable at an operating spin-rate during the operation mode of the disk drive. The commutation state sequencer includes a sequence of commutation states for generating a sequence of control signals. The sequence of commutation states includes a present commutation state and a next commutation state. The switching elements are responsive to the sequence of control signals for sequentially applying a voltage across a selected combination of the windings to generate a torque on the rotor in order to maintain, the operating spin-rate. The spindle motor control system provides a series of commutation clock pulses to advance the commutation state sequencer from the present commutation state to the next commutation state. The series of commutation clock pulses have a corresponding series of commutation clock periods. At least two of the commutation clock periods each have a systematically introduced variation from a nominal commutation clock period that depends on the operating spin-rate. The systematically introduced variation for each of the at least two commutation clock periods reduces the acoustic noise in the disk drive.
The invention can also be regarded as a method of reducing acoustic noise in a disk drive that incidentally generates undesirable acoustic noise during an operation mode. The disk drive includes a spindle motor having a plurality of windings and a rotor rotatable at an operating spin-rate during the operation mode of the disk drive; and a spindle motor driver having switching elements. The method includes providing a sequence of commutation states for generating a sequence of control signals. The sequence of commutation states include a present commutation state and a next commutation state. The method also includes controlling the switching elements with the sequence of control signals to sequentially apply a voltage across a selected combination of the windings to generate a torque on the rotor in order to maintain the operating spin-rate. The method also includes providing a series of commutation clock pulses to advance the sequence of commutation states from the present commutation state to the next commutation state. The series of commutation clock pulses have a corresponding series of commutation clock periods. The method also includes systematically introducing variation from a nominal commutation clock period that depends on the operating spin-rate into each of at least two of the commutation clock periods to reduce the acoustic noise in the disk drive.